(1) Field of the Invention
The present invention relates to a polymer of 4-methylpentene-1 having a substantially syndiotactic structure and high tacticity.
(2) Description of the Prior Art
Polymers of .alpha.-olefin having a syndiotactic structure have been known for a long period of time, and one of them is syndiotactic polypropylene. However, the syndiotactic polypropylene, which can be obtained by a method for polymerizing propylene at a low temperature in the presence of a catalyst comprising a vanadium compound, an ether and an organic aluminum compound, is poor in syndiotacticity. For this reason, such a kind of polypropylene is not considered to have the characteristics of syndiotactic polypropylene.
J. A. Ewen et al. have found for the first time that when propylene is polymerized by the use of a polymerization catalyst comprising a transition metal (Hf or Zr) compound having an asymmetric ligand and methyl aluminoxane, a propylene having such a good tacticity that a syndiotactic pentad fraction measured by .sup.13 C-NMR in excess of 0.7 can be obtained [J. Amer. Chem. Soc., 110, 6255-6256 (1988)].
In the J. A. Ewen et al. method, the activity of each transition metal is high, and the syndiotactic polypropylene obtained by this method has high syndiotacticity and excellent physical properties. However, J. A. Ewen et al. do not disclose the polymerization of 4-methylpentene-1 at all.
It is known that some of the polymers of 4-methylpentene-1 are isotactic or atactic, and the polymers of 4-methylpentene-1 having the syndiotactic structure have also been reported by A. Zambelli et al. [Macromolecules, 22, 2126-2128 (1989)]. The A. Zambelli et al. method comprises hydrogenating a 1,2-polymer of 4-methyl-1,3-pentadiene having the syndiotactic structure in order to prepare the polymer of 4-methylpentene-1 having the syndiotactic structure.
However, the tacticity of the 1,2-polymer is not high, and thus the polymer of 4-methylpentene-1 which is the hydrogenated compound thereof is also poor in tacticity, with the result that the polymer of 4-methylpentene-1 has low crystallizability. I addition, the A. Zambelli et al. method has the drawback that a copolymer of 4-methylpentene-1 and another .alpha.-olefin cannot be prepared by this method.